The present disclosure relates to subject matter contained in Japanese Patent Application No. 3-232573 (filed on Jun. 5, 1991), which is expressly incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a distal end part of an endoscope in which the surfaces of illuminating and viewing windows, which are provided in a side by side in the distal end of an insert part of the endoscope, are covered with a transparent cover.
2. Description of the Prior Art
FIG. 4 shows the distal end part of an endoscope according to a prior art. Reference numeral 51 denotes a distal end block that is provided at the distal end of an insert part of the endoscope. A continuous transparent cover 52 is provided at the distal end of a sheath for removably covering the insert part of the endoscope.
Illuminating light, that is emitted from an illuminating window 53 provided in the distal end block 51, passes through the transparent cover 52 and illuminates an object. Light reflected from the object enters an objective optical system 54a through a viewing window 54, so that an image of the object is formed on an entrance end face 55a of an image guide fiber bundle 55.
However, if the illuminating and viewing windows 53 and 54, which are disposed in a side by side, are covered with the transparent cover 52, part of the illuminating light emitted from the illuminating window 53 is reflected at the inner side of the surface of the transparent cover 52 and thus transmitted therethrough, as shown in FIG. 5. The transmitted light shines brightly on the chamfered portion or edge portion of the outer edge portion 57 of a window glass 56 provided in the viewing window 54.
Consequently, light from the brightened outer edge portion 57 of the window glass 56 is further reflected at the inner side of the surface of the transparent cover 52 and enters the visual field of the objective optical system 54a, thus producing an adverse effect on the observed image. In other words, since the virtual images 56a and 57a of the window glass 56 and its outer edge portion 57, which are produced by reflection, are formed within the visual field A, as shown by the chain line in FIG. 5, the bright virtual image 57a of the outer edge portion 57 is undesirably observed.